Data processing method and apparatus for a display device

ABSTRACT

With the new plasma display panel technology new kinds of artefacts can occur in video pictures due to the principle that brightness control is done with a modulation of small lighting pulses in a number of periods called sub-fields. These artefacts are commonly described as ‘dynamic false contour effect’. To compensate for this effect motion estimators are used and with the resulting motion vectors corrected sub-field code words are calculated for the critical pixels. Today&#39;s motion estimators work with the luminance signal component of the pixels. This is not sufficient for plasma displays. It is therefore proposed to make the motion vector calculation separately for the color components and with either the sub-field code words as data input or with single bit data input for performing motion estimation separately for single sub-fields or for a sub-group of bits from the sub-field code words. The proposal also concerns apparatuses for performing the inventive method.

This application claims the benefit, under 35 U.S.C. § 365 ofInternational Application PCT/EP00/09452, filed Sep. 27, 2000, which waspublished in accordance with PCT Article 21(2) on Apr. 5, 2001 inEnglish and which claims the benefit of European patent application No.99250346.6 filed Sep. 29, 1999.

The invention relates to a method and apparatus for processing videopictures for display on a display device. More specifically theinvention is closely related to a kind of video processing for improvingthe picture quality of pictures which are displayed on matrix displayslike plasma display panels (PDP) or other display devices where thepixel values control the generation of a corresponding number of smalllighting pulses on the display.

BACKGROUND

The Plasma technology now makes it possible to achieve flat colour panelof large size (out of the CRT limitations) and with very limited depthwithout any viewing angle constraints.

Referring to the last generation of European TV, a lot of work has beenmade to improve its picture quality. Consequently, a new technology likethe Plasma one has to provide a picture quality as good or better thanstandard TV technology. On one hand, the Plasma technology gives thepossibility of “unlimited” screen size, of attractive thickness, etc.But on the other hand, it generates new kinds of artefacts, which couldreduce the picture quality.

Most of these artefacts are different as for TV pictures and that makesthem more visible since people are used to seeing old TV artefactsunconsciously.

The artefact, which will be presented here, is called “dynamic falsecontour effect” since it corresponds to disturbances of grey levels andcolours in the form of an apparition of coloured edges in the picturewhen an observation point on the PDP screen moves. The degradation isenhanced when the image has a smooth gradation like a skin. This effectleads to a serious degradation of the picture sharpness, too.

FIG. 1 shows the simulation of such a false contour effect on a naturalscene with skin areas. On the arm of the displayed woman are shown twodark lines, which e.g. are caused by this false contour effect. Also inthe face of the woman such dark lines occur on the right side.

In addition, the same problem occurs on static images when observers areshaking their heads and that leads to the conclusion that such a failuredepends on the human visual perception and happens on the retina.

Some algorithms are known today, which are based on motion estimation invideo pictures in order to be able to anticipate the motion of thecritical observation points to reduce or suppress this false contoureffect. In most cases, these different algorithms are focused on thesub-field coding part without giving detailed information concerning themotion estimators used.

In the past, the motion estimator evolution was mainly focused onflicker-reduction for European TV pictures (e.g. with 50 Hz to 100 Hzupconversion), for proscan conversion, for motion compensated pictureencoding like MPEG-encoding and so one. For that purpose, thesealgorithms are working mainly on luminance information and above allonly on video level information. Nevertheless, the problems that have tobe solved for such applications are different from the PDP dynamic falsecontour issue, since the problems are directly linked to the way thevideo information is encoded in plasma displays.

A lot of solutions have been published concerning the reduction of thePDP false contour effect based on the use of a motion estimator.However, such publications do not mention the topic of motion estimatorsand especially its adaptation to specific plasma requirements.

A Plasma Display Panel (PDP) utilizes a matrix array of discharge cellsthat could only be “ON” or “OFF”. Also unlike a CRT or LCD in which greylevels are expressed by analog control of the light emission, a PDPcontrols the grey level by modulating the number of light pulses perframe. This time-modulation will be integrated by the eye over a periodcorresponding to the eye time response.

When an observation point (eye focus area) on the PDP screen moves, theeye will follow this movement. Consequently, it will no more integratethe light from the same cell over a frame period (static integration)but it will integrate information coming from different cells located onthe movement trajectory and it will mix all these light pulses togetherwhich leads to a faulty signal information.

Today, a basic idea to reduce this false contour effect is to detect themovements in the picture (displacement of the eye focus area) and toapply different type of corrections over this displacement in order tobe sure the eye will only perceive the correct information through itsmovement. These solutions are described e.g. in EP-A-0 980 059 andEP-A-0 978 816 that are published European Patent Applications of theapplicant.

Nevertheless, in the past, the motion estimator evolution was mainlyfocused on other applications than Plasma technology and the aim of afalse contour compensation needs some adaptation to plasma specificrequirements.

In fact, standard motion estimators work on video level basis andconsequently they are able to catch a movement on a structure appearingat this video level (e.g. strong spatial gradient). If an error has beenmade on a homogeneous area, this will have no impact on standard videoapplication like proscan conversion since the eye will not see anydifferences in the displayed video level (analog signal on CRT screen).On the other hand, in the case of a plasma screen, a small difference inthe video level can come from a big difference in the light pulseemission scheme and this can cause strong false contour artefacts.

Invention

It is therefore an object of the present invention to disclose anadapted standard motion estimator for matrix displays like plasmadisplay appliances. That is the key issue of this invention, which couldbe used for each kind of Plasma technology at each level of itsdevelopment (even if the scanning mode and sub-field distribution is notwell defined).

According to claim 1 the invention concerns a method for processingvideo pictures for display on a display device having a plurality ofluminous elements corresponding to the pixels of a picture, wherein thetime duration of a video frame or video field is divided into aplurality of sub-fields (SF) during which the luminous elements can beactivated for light emission in small pulses corresponding to asub-field code word which is used for brightness control, wherein toeach sub-field a specific sub-field weight is assigned, wherein motionvectors are calculated for pixels and these motion vectors are used todetermine corrected sub-field code words for pixels, characterized inthat, a motion vector calculation is being made separately for one ormore colour component (R,G,B) of a pixel and wherein for the motionestimation the sub-field code words are used as data input, and whereinthe motion vector calculation is done separately for single sub-fieldsor for a sub-group of sub-fields from the plurality of sub-fields, orwherein the motion vector calculation is done based on the completesub-field code words and the sub-field code words being interpreted asstandard binary numbers.

Further advantageous measures are apparent from the dependent claims.

The invention consists also in advantageous apparatuses for carrying outthe inventive method.

In one embodiment the apparatus for performing the method of claim 1,has a sub-field coding unit for each colour component video data, andcorresponding compensation blocks (dFCC) for calculating correctedsub-field code words based on motion estimation data, and ischaracterized in that, the apparatus further has corresponding motionestimators (ME) for each colour component and that the motion estimatorsreceive as input data the sub-field code words for the respective colourcomponents.

In another embodiment the apparatus for performing the method of claim1, has a sub-field coding unit for each colour component video data, andis characterized in that, the apparatus further has motion estimatorsfor each colour component and the motion estimators are sub-divided in aplurality of single bit motion estimators (ME) which receive as inputdata a single bit from the sub-field code words for performing motionestimation separately for single sub-fields and that the apparatus has acorresponding plurality of compensation blocks (dFCC) for calculatingcorrected sub-field code word entries.

In a third embodiment the apparatus for performing the method of claim1, has a sub-field coding unit for each colour component video data, andis characterized in that, the apparatus further has motion estimatorsfor each colour component and the motion estimators are single bitmotion estimators which receive as input data a single bit from thesub-field code words for performing motion estimation separately forsingle sub-fields and that the apparatus has corresponding compensationblocks (dFCC) for calculating corrected sub-field code word entries andwherein the motion estimators and compensation blocks are usedrepetitively during a frame period for the single sub-fields.

DRAWINGS

Exemplary embodiments of the invention are illustrated in the drawingsand are explained in more detail in the following description.

In the figures:

FIG. 1 shows a video picture in which the false contour effect issimulated;

FIG. 2 shows an illustration for explaining the sub-field organizationof a PDP;

FIG. 3 shows an example of a sub-field organisation with 10 sub-fields;

FIG. 4 shows an example of a sub-field organisation with 12 sub-fields;

FIG. 5 shows an illustration for explaining the false contour effect;

FIG. 6 illustrates the appearance of a dark edge when a display of twoframes is being made in the manner shown in FIG. 5;

FIG. 7 shows an illustration for explaining the false contour effectappearing due to display of a moving black-white transition;

FIG. 8 illustrates the appearance of a blurred edge when a display oftwo frames is being made in the manner shown in FIG. 7;

FIG. 9 illustrates the block matching process in motion estimatorsworking on video level or luminance basis;

FIG. 10 illustrates the result of the block matching operation shown inFIG. 9;

FIG. 11 illustrates that motion estimators relying on luminance valuescannot estimate motion in specific cases;

FIG. 12 illustrates the calculation of binary gradients in case of a127/128 transition and standard 8 bit coding;

FIG. 13 illustrates the calculation of binary gradients in case of a127/128 transition and 12 sub-field coding;

FIG. 14 depicts a block diagram for an apparatus for false contoureffect reduction with motion estimation on each colour component;

FIG. 15 shows a video picture according to 8 bit values of the colourcomponents;

FIG. 16 shows the same video picture as in FIG. 15 but with differentvideo levels derived from the sub-field code words;

FIG. 17 shows extracted edges from the video picture shown in FIG. 15where the colour components are represented first with 8 bit values andsecond with 12 bit sub-field code words;

FIG. 18 shows a decomposition of a picture in pictures corresponding tosingle sub-field data;

FIG. 19 shows motion estimation in the picture with sub-field data SF4from FIG. 18;

FIG. 20 shows a block diagram for an apparatus for false contour effectreduction with separate motion estimation for single sub-fields;

FIG. 21 shows a further block diagram for an apparatus for false contoureffect reduction;

EXEMPLARY EMBODIMENTS

As previously said, a Plasma Display Panel (PDP) utilizes a matrix arrayof discharge cells that can only be “ON” or “OFF”. In a PDP the pixelcolours are produced by modulating the number of light pulses of eachplasma cell per frame period. This time modulation will be integrated bythe eye over a period corresponding to the human eye time response.

In TV technology an 8-bit representation of the video levels for the RGBcolour components is very common. In that case is each level will berepresented by a combination of the 8 following bits:

-   -   1-2-4-8-16-32-64-128

To realize such a coding with the PDP technology, the frame period willbe divided in 8 lighting periods (called sub-fields), each onecorresponding to a bit. The number of light pulses for the bit “2” isthe double as for the bit “1” and so on. With these 8 sub-periods, it ispossible through combination, to build the 256 different video levels.Without motion, the eye of the observers will integrate over about aframe period these sub-periods and catch the impression of the rightgrey level. FIG. 2 represents this decomposition. In this figure theaddressing and erasing periods of every sub-field are not shown. Theplasma driving principle however requires also these periods. It is wellknown to the skilled man, that during each sub-field a plasma cell needsto be addressed, first in an addressing or scanning period, afterwardsthe sustain period follows where the light pulses are generated andfinally in an erase period the charge in the plasma cells is quenched.

This PWM-type light generation introduces new categories ofimage-quality degradation corresponding to disturbances of grey levelsor colours. The name for this effect is dynamic false contour effectsince the fact that it corresponds to the apparition of coloured edgesin the picture when an observation point on the PDP screen moves. Suchfailures on a picture lead to an impression of strong contours appearingon homogeneous area like skin. The degradation is enhanced when theimage has a smooth gradation and also when the light-emission periodexceeds several milliseconds. In addition, the same problems occur onstatic images when observers are moving their heads and that leads tothe conclusion that such a failure depends on the human visualperception.

In order to improve the picture quality of moving images, sub-fieldorganisations with more than 8 sub-fields are used today. FIG. 3 showsan example of such a coding scheme with 10 sub-fields and FIG. 4 showsan example of a sub-field organisation with 12 sub-fields. Whichsub-field organisation is best to be taken, depends on the plasmatechnology. Some experiments are advantageous with this respect.

For each of these examples, the sum of the weights is still 255 but thelight distribution of the frame duration has been changed in comparisonto the previous 8-bit structure. This light emission pattern introducesnew categories of image-quality degradation corresponding todisturbances of grey levels and colours. These will be defined asdynamic false contour since the fact that it corresponds to theapparition of coloured edges in the picture when an observation point onthe PDP screen moves. Such failures on a picture lead to an impressionof strong contours appearing on homogeneous areas like skin and to adegradation of the global sharpness of moving objects. The degradationis enhanced when the image has a smooth gradation and also when thelight-emission period exceeds several milliseconds.

In addition, the same problems occur on static images when observers areshaking their heads and that leads to the conclusion that such a failuredepends on the human visual perception.

As already said, this degradation has two different aspects:

-   -   on homogeneous areas like skin, it leads to an apparition of        coloured edges;    -   on sharp edges like object borders, it leads to a blurred effect        reducing the global picture sharpness impression.

To understand a basic mechanism of visual perception of moving images,two simple cases will be considered corresponding to each of the twobasis problems (false contouring and blurred edges). These twosituations will be presented in the case of the following 12 sub-fieldencoding scheme:

-   -   1-2-4-8-16-32-32-32-32-32-32-32

First case considered, is a transition between the level 128 and 127moving at 5 pixel per frame, the eye following this movement. This caseis shown in FIG. 5.

FIG. 5 represents in light grey the lighting sub-fields corresponding tothe level 127 and in dark grey, these corresponding to the level 128.

The diagonal parallel lines originating from the eye indicate thebehaviour of the eye integration during a movement. The two outerdiagonal eye-integration-lines show the borders of the region withfaulty perceived luminance. Between them, the eye will perceive a lackof luminance, which leads to the appearing of a dark edge as indicatedin the eye stimuli integration curve at the bottom of FIG. 5.

In case of a grey scale picture this effect corresponds to theapparition of artificial white or black edges. In the case of colouredpictures, since this effect will occur independently on the differentcolour components, it will lead to the apparition of coloured edges inhomogeneous areas like a skin. This is also illustrated in FIG. 6 forthe same moving transition.

Second case considered is a pure black to white transition between thelevel 0 and 255 moving at 5 pixel per frame, the eye following thismovement. This case is depicted in FIG. 7. The figure represents in greythe lighting sub-fields corresponding to the level 255.

The two extreme diagonal eye-integration-lines show again the borders ofthe region where a faulty signal will be perceived. Between them, theeye will perceive a growing luminance, which leads to the appearing of ashaded or blurred edge. This is shown in FIG. 8.

Consequently, the pure black to white transition will be lost during amovement and that leads to a reduction of the global picture sharpnessimpression.

As explained above, the false contour effect is produced on the eyeretina when the eye follows a moving object since the eye does notintegrate the right information at the right time. There are differentmethods to reduce such an effect but the more serious ones are based ona motion estimator (dynamic methods), which aim to detect the movementof each pixel in a frame in order to anticipate the eye movement or toreduce the failure appearing on the retina through differentcorrections.

In other words, the goal of each dynamic algorithm is to define for eachpixel observed by the eye, the way the eye is following its movementduring a frame in order to generate a correction on this trajectory.Such algorithms are described e.g. in EP-A-0 980 059 and EP-A-0 978 816which are European patent applications of the applicant.

Consequently, for each pixel of the frame N, we will dispose of a motionvector {right arrow over (V)}=(V_(x);V_(y)), which describes thecomplete motion of the pixel from the frame N to the frame N+1, and thegoal of a false contour compensation is to apply a compensation on thecomplete trajectory defined by this vector.

In the following, it is not focused on the compensation itself butmerely on the motion estimation. For the compensation of the falsecontour effect it is referred to a method using sub-field shiftingoperation in the direction of the motion vector for the pixels in acritical area. The corresponding sub-field shifting algorithm isdescribed in detail in EP-A-0 980 059. For the disclosure regarding thisalgorithm it is therefore expressively referred to this document. Ofcourse, there exist some other algorithms for false contour effectreduction, but the sub-field shifting algorithm gives very promisingresults.

Such a compensation applied to moving edges will improve its sharpnesson the eye retina and the same compensation applied to movinghomogeneous areas will reduce the appearance of coloured edges.

It is however, expressively mentioned that such a compensation principleneeds motion information from a motion estimator for both kind of areas:homogeneous ones and object borders. In fact, today, the standard motionestimators are working on luminance signal video level. It is well knownto the skilled man that the luminance signal Y is a combination of thesignals for the three colour components. The following equation is takento generate the luminance signal:U _(Y)=0.3U _(R)+0.5U _(G)+0.11U _(B)

Based on the luminance signal it is possible to reliably detect themotion of edges but it is much more difficult to detect the motion of anhomogeneous area.

In order to understand more clearly this problem, a simple example willbe presented, the case of a ball moving on a white screen from the frameN to the frame N+1. Standard motion estimators try to find a correlationbetween a sub-part of the first picture (frame N) and a sub-part of thesecond picture (frame N+1). The size, form and type of these subpartsdepend on the motion estimator type used (block matching, pel recursive,etc.). Widely used are block matching motion estimators. A simple blockmatching process will be studied in order to show the problematic. Inthat case, each frame will be subdivided in blocks and a matching willbe searched between blocks from two consecutive frames in order tocompute the movement of the ball.

As shown in FIG. 9 the ball in frame N will be subdivided in 25 blocks.The position of the ball in the next frame N+1 is indicated with thedashed circle.

The best matches with the 25 pixel blocks in frame N+1 are shown in FIG.10. The blocks having a unique match are indicated with the same numberas in the frame N, the blocks having no match are represented with an“x” and the block with more than one match (no defined motion vector)are represented with a “?”.

In the undefined area represented with “?” these motion estimatorsworking on luminance signal level have no chance to find a precisemotion vector, since the video level is about the same in all theseblocks (e.g. video levels from 120 to 130). Some estimators will producefrom such areas very noisy motion vectors or will declare these areas asnon-moving areas.

Nevertheless, it was explained that a transition 127/128 definitelyproduces a severe false contour effect and consequently it is importantto compensate also such areas and for that purpose a precise motionfield is needed at this location.

For that reason, there is a lack of information coming from standardmotion estimators and therefore such kind of motion estimators need anadaptation to the new plasma requirements.

According to the invention there is proposed an adaptation of the motionestimators, which is based on two ideas.

The first idea can be summarized: “Detection based on separate colourcomponents.”

In the previous paragraphs, the false contour explanations have shownthat the false contour effect appears separately on the three colourcomponents. Consequently it seems important to compensate separately thedifferent colour components and to do that, independent motion vectorsfor the three colour components are required.

In order to support this affirmation, the example of a magenta-likesquare moving on a cyan-like background is presented.

The magenta-like colour is made for instance with the level 100 in BLUEand RED and without GREEN component. The cyan-like colour is made forinstance with the level 100 in BLUE and 50 in GREEN and without REDcomponent.

The luminance signal level 40 is for both colours identical. There is nodifference at all on luminance signal basis between the moving squareand the background. The whole picture has got the same luminance level.Consequently, each motion estimator working on luminance values onlywill not be able to detect a movement.

The eye itself will detect a movement and will follow this movement andthat leads to a false contour effect appearing at the square transitionsfor the green and red components only.

In fact, the blue component is homogeneous in the whole picture and forthat reason, no false contour is produced in this component.

For this example it is therefore necessary to estimate the motion in thepicture based on the components RED and GREEN and not for the blue one.It is evident, that in the general case it is an improvement for motionestimation to make the motion estimation for the three colour componentsseparately.

The second aspect of the invention for an adaptation of the motionestimation can be summarized: “Detection based on sub-field level”.

In the previous paragraphs, the false contour explanations have shownthat a transition 127/128 will produce a false contour effect, whichcould be very disturbing for the eye. Since this false contour effectoccurs in transitions which are almost invisible at the luminance signallevel, it is likely that the motion vectors determined for this area arefalse and as a consequence the compensation itself will not workproperly.

Nevertheless, if the sub-field code words of a colour component are usedfor motion estimation, this makes a big difference. Using the example ofthe sub-field encoding based on 12 sub-fields(1-2-4-8-16-32-32-32-32-32-32-32) the video levels 127 and 128 can berepresented as following:

Standard 8 bit 12 bit coded value Corresponding 12 bit video Level (MSB

LSB) video level 127 (01111111) 000011111111 255 128 (10000000)000111100000 480

Consequently, a motion estimator working on each colour component afterthe sub-field encoding will dispose of more bit information and will beable to compensate more precisely the false contour effect appearing inthe homogeneous areas.

As already said in the previous parts of this document, all motionestimators focus their estimation on the movement of structures orgradients which are easy to estimate and then try to extend thisestimation to neighbourhood areas.

It is therefore a further aspect of the invention to redefine the notionof gradient since the false contour failure appears at sub-field leveland not at video level.

Again the example of the gradient on video level for the transition127/128. This gradient has an amplitude of 1 (128−127) but if we take alook on the bit changing, we can see that even with an 8 bit coding allbits are different between these two values. In case of 12-bit sub-fieldencoding, there is a difference in 6 bits between the two values.Consequently, it is an improvement if the gradient refers to the bitchanging between two values and not to the level changing between them.In addition, it is evident that the failure appearing on the retina incase of moving pictures depends on the weight of the sub-fields thatwill be faulty integrated. For that reason, it is proposed to define anew type of gradients called “binary gradients”, through the bitchanging at sub-field level, each bit being weighted by its sub-fieldweight. These new binary gradients need to be detected in the picture.This definition of binary gradients aims to focus the motion estimationon the sub-field changing areas and not on the video level changingareas.

The building of binary gradients according to the new definition isillustrated in FIGS. 12 and 13 for the transition 127/128 with differentsub-field coding schemes. In FIG. 12 the standard B-bit coding scheme isused and in FIG. 13 the specific 12-bit encoding scheme is used.

With 8 bit encoding scheme, the binary-gradient has the value 255 which,in that case, corresponds to the maximum amplitude of the false contourfailure, which could appear at such a transition.

With this 12 bit sub-field encoding, the binary-gradient has a value of63. It is evident from this that the 12 bit sub-field organisation isless susceptible to the false contour effect.

These two previous examples show the way a plasma adapted motionestimator can be improved in order to focus on the detection of criticalmoving transitions for the false contour problem. FIG. 14 shows a blockdiagram for an adapted false contour compensation apparatus.

The inputs in this embodiment are the three colour components at videolevel and the outputs are the compensated sub-field-code words for eachcolour component, which will be sent to the addressing control part ofthe PDP. The information Rx and Ry corresponds to the horizontal andvertical motion information for the Red component, Gx and Gy for thegreen, Bx and By for the blue component.

In order to understand more precisely the reasons of this motiondetection based on sub-fields information, an example of a natural TVsequence has been chosen. This sequence is naturally blurred and thatleads to large homogeneous areas and to a lack of information at videolevel for a standard motion estimation on these areas as seen on thepicture of FIG. 15.

On the other hand, the same picture represented on sub-fields level(with 12 bit), where each sub-field code word is interpreted as a binarynumber, will provide more information in these critical areas. Thecorresponding sub-field picture is shown in FIG. 16.

In the picture of FIG. 16 a lot of new regions appear in the face of thewoman. These correspond to a different sub-field structure andconsequently their borders (sub-field transitions) are the location offalse contour effect appearance like in the example 127/128 transitionmentioned above. For that reason, an improvement can be achieved, if aplasma dedicated motion estimator has to provide a precise motion vectorof such sub-field transitions.

In fact, the most motion estimators today are working on the detectionof moving gradients (e.g. pel recursive) and moving structures (e.g.block matching) and a comparison of the extracted edges from the twoprevious pictures shows the improvement introduced through an analysison sub-fields level. This is shown in FIG. 17.

The lower picture in FIG. 17 represents standard edges extracted from a12-bit picture. It is obvious that there is much more information in theface for a motion estimator. All these edges are real critical ones forthe false contour effect and should be properly compensated.

As a conclusion, it is evident that there are two possibilities toincrease the quality of a motion estimator at sub-fields level. Thefirst one is to use a standard motion estimator but replacing its videoinput data with sub-field code word data (more than 8 bit). This willincrease the amount of available information but the gradients used bythe estimators will stay standard ones. A second possibility to furtherincrease its quality is to change the way of comparing pixels e.g.during block matching. If the so-called binary-gradients, as defined inthis document are computed, then the critical transitions are easilyfound.

There is another possibility to further improve the quality of themotion estimation according to this invention. It consists in aseparately motion estimation of each sub-field. In fact, since the falsecontour effect appears on the sub-field level, it is proposed tocompensate the movement of sub-fields. For that purpose an estimation ofthe movement in the picture for each sub-field separately could be aserious advantage.

In this case a picture based on a certain sub-field code word entry is abinary picture containing only binary data 0 or 1 as pixel values. Sincethe fact that only the higher sub-field weights will cause seriouspicture damages, the motion detection can concentrate on the mostsignificant sub-fields, only. This is illustrated in FIG. 18. Thisfigure represents the decomposition of one original picture in 9sub-field pictures. The sub-field organisation is one with 9 sub-fieldsSF0 to SF8. In the picture for sub-field 0, there is not much structureof the original picture seen. The sub-field data represent some veryfine details that do not allow to see the contours in the picture. It isremarked, that the picture is presented with all three colourcomponents. Also in the pictures for sub-fields SF1 to SF3 the picturestructure is not seen clear enough. However, the transitions on the arm(which are false contour critical) appear already in the sub-fieldpicture for sub-field SF2 and after. Especially this structure is verygood viewable in the picture for sub-field SF4. Therefore, motionestimation made based on SF4 data, will deliver very good results forfalse contour compensation. This is further illustrated in FIG. 19. Thepicture for sub-field SF4 is shown in the upper part. In the lower part,the corresponding picture 5 frames later is shown. From these picturesit is obvious that it is possible to estimate the movement of two blockslocated on some given structure in the picture reliably. In that case,with a simple motion estimator (e.g. block matching, pel recursive) itis possible to determine the movement of the sub-fields between twoconsecutive frames and to modify its position depending on its real timeposition in the frame.

In that case, simple motion estimators are used in parallel since theyare working on 1 bit-pictures, only. This will be done to extract fromeach single sub-field picture a motion vector field, which will be usedfor the compensation in the corresponding sub-field. Practicallyspeaking, for each pixel and each sub-field a motion vector iscalculated. The motion vector then is used to determine a sub-fieldentry shift for compensation. The sub-field shifting calculation can bedone as explained in EP-A-0 980 059. The center of gravity of thesub-field needs to be taken into account as disclosed there.

FIG. 20 shows a block diagram for this embodiment.

In this block diagram, a compensation based on the 8 most significantsub-fields in the case of a 12 sub-fields encoding has been represented.Only these 8 MSBs will be estimated with a simple motion estimator basedon 1-bit pictures, and then compensated.

One big advantage of such a principle is the strong reduction ofcomplexity for the motion estimators (less on-chip memory, simplermemory management, very simple computations). In fact the die-size willbe reduced since each line memory needed by the motion estimator willcorrespond to a pixel depth of 1 bit only (low resources on-chip).

In addition, in case of the ADS addressing scheme (Address DisplaySeparately), the memory management will be simplified since thestructure of ADS needs to store separately the different sub-fields in asub-field memory. These sub-fields, will be read each after the other tobe displayed on the screen. Obviously, the compensation can be made atthis processing stage, i.e. after having the 1 bit sub-field picturesmemorised. This allows to use only one motion estimator with 1 bit depthfor all 1 bit sub-field pictures. This solution is disclosed in theblock diagram of FIG. 21. In this block diagram, video data is input toa video processing unit in which all video processing steps based on 8bit video data is performed such as interlace proscan conversion, colourtransition improvement, edge replacement, etc. The video data of eachcolour component is then sub-field encoded in the sub-fields encodingblock according to a given sub-field organisation e.g. the one shown inFIG. 3 with 10 sub-fields. The sub-field code word data are thenre-arranged in the sub-fields re-arrangement block. This means that incorresponding sub-field memories, all the data bits of the pixels forone dedicated sub-field are stored. There need to be as much sub-fieldmemories as sub-fields are present in the sub-field organisation. In thecase of 10 sub-fields in the sub-field organisation, this means 10sub-field memories are required for storing the sub-field code words forone picture.

The motion estimation is performed in this arrangement for the selectedsub-fields separately. As motion estimators need to compare at least twosuccessive pictures, there is the need of some more sub-field memoriesfor storing the data of the previous or next picture.

The sub-field code word bits are forwarded to the dynamic false contourcompensation block dFCC together with the motion vector data. Thecompensation is carried out in this block e.g. by sub-field entryshifting as explained above.

In this architecture, there is only the need of one 1-bit motionestimator, which can be used for all sub-fields. It is however remarked,that there are sub-field code words for each colour components and thattherefore there is the need to have the components sub-field encoding,sub-field rearrangement, sub-field memory, motion estimation and dFCC intriplicate.

There are a number of modifications possible to the disclosed invention.E.g. one variation is to make the motion estimation on a selected groupof sub-fields in the sub-field organisation instead of singlesub-fields, separately. E.g. it could be possible to make the motionestimation based on two bit code words for the sub-fields 3 and 4 in oneembodiment. The compensation for those sub-fields is then being donewith the motion vector for the group of sub-fields. This is also anembodiment according to this invention.

Another modification is to calculate an average motion vector from allthe motion vectors for the single or grouped sub-fields before applyingthe compensation. Also this is a further embodiment according to thisinvention.

1. Method for processing video pictures for display on a display devicehaving a plurality of luminous elements corresponding to the pixels of apicture, wherein the time duration of a video frame or video field isdivided into a plurality of sub-fields during the luminous elements canbe activated for light emission in small pulses corresponding to asub-field code word which is used for brightness control, wherein toeach sub-field a specific sub-field weight is assigned, wherein thevideo signals for the pixels of a picture are sampled, said video signalsamples are represented by video data words having N bits, wherein tothe video data words sub-field code words are assigned having N+X bits,N and X being integer numbers, wherein with motion estimation motionvectors are calculated for pixels in a video picture, and these motionvectors are used to determine corrected sub-field code words for pixels,wherein, a motion vector calculation is being made separately for one ormore colour components of a pixel, wherein for the motion vectorcalculation the sub-field code words having N+X bits are used as datainput instead of the video data words having N bits for a colourcomponent, and wherein the motion vector calculation is done based onthe complete sub-field code words or based on code words that are formedfrom the entries in the sub-field code words of only a sub-group ofsub-fields from the plurality of sub-fields and the motion vectordefines a trajectory along which corrected sub-field code words will beplaced.
 2. Method according to claim 1, wherein for the case that amotion vector calculation is done based on the complete sub-field codewords or for a sub-group of sub-fields, a gradient determination step isperformed for comparing pixels in two successive frames, with thegradient between two pixels being defined as the sum of the sub-fieldweights of those sub-fields of the sub-field code words or sub-group ofthe sub-field code words which have different binary entries.
 3. Methodfor processing video pictures for display on a display device having aplurality of luminous elements corresponding to the pixels of a picture,wherein the time duration of a video frame or video field is dividedinto a plurality of sub-fields during which the luminous elements can beactivated for light emission in small pulses corresponding to asub-field code word which is used for brightness control, wherein toeach sub-field a specific sub-field weight is assigned, wherein motionvectors are calculated for pixels in a video picture, and these motionvectors are used to determine corrected sub-field code words for pixels,wherein, a motion vector calculation is being made separately for one ormore colour component of a pixel, and for the motion vector calculationthe sub-field code words are used as data input instead of the videosignal samples for a colour component, and wherein a motion vectorcalculation is done based on a single bit picture, wherein each pixel ofthe single bit picture is equal to a dedicated entry of thecorresponding sub-field code word for that pixel, namely the entry for adedicated single sub-field from the plurality of sub-fields.
 4. Methodaccording to claim 3, wherein the resulting motion vector calculatedbased on a single bit picture is used to calculate corrected sub-fieldcode word entries for only the sub-field based on which the motionvector calculation has been made.
 5. Method according to claim 3,wherein motion vectors are calculated separately for those sub-fieldshaving the higher sub-field weights.
 6. Method according to claim 3,wherein the resulting motion vectors calculated from single bit picturesfor a pixel are averaged and the averaged motion vector is used tocalculate corrected sub-field code word entries for the sub-field codewords.
 7. Method according to claim 1, wherein for the determination ofcorrected sub-field code words sub-field entry shifts are calculated fora given pixel based on the calculated motion vector and wherein thesub-field entry shifts determine which sub-field entry in the sub-fieldcode word of a given pixel need to be shifted to which pixel positionalong the direction of the motion vector.
 8. Method according to claim1, wherein it is used in a plasma display device for dynamic falsecontour compensation.
 9. Apparatus for performing the method of claim 3,having a sub-field coding unit for each colour component video data,wherein, the apparatus further has motion estimators for each colourcomponent and the motion estimators are sub-divided in a plurality ofsingle bit motion estimators which receive as input data the single bitpixels from the sub-field code words for performing motion estimationseparately for a single sub-field and that the apparatus has acorresponding plurality of compensation blocks for calculating correctedsub-field code word entries.
 10. Apparatus for performing the method ofclaim 1, having a sub-field coding unit for each colour component videodata, and corresponding compensation blocks for calculating correctedsub-field code words based on motion vector data, characterized in that,the apparatus further has corresponding motion estimators for eachcolour component and that the motion estimators receive as input datathe sub-field code words having N+X bits instead of the video data wordshaving N bits for the respective colour components.
 11. Method forprocessing video pictures for display on a display device having aplurality of luminous elements corresponding to the pixels of a picture,wherein the time duration of a video frame or video field is dividedinto a plurality of sub-fields during which the luminous elements can beactivated for light emission in small pluses corresponding to asub-field code word which is used for brightness control, wherein toeach sub-field a specific sub-field wieght is assisgned, wherein thepixels are represented by video data words having N bits, wherein to thevideo data words sub-field code words are assigned having N + X bits, Nand X being integer numbers, wherein with motion estimation motionvectors are calculated for pixels in a video picture, and these motionvectors, are used to determine corrected sub-field code words forpixels, wherein, a motion vector calculation is being made separatelyfor one or more clour components of a pixel, wherein for the motionvector calculation the complete sub-field code words having N + X bitsor code words that are formed from the entries in the sub-fields codewords of only a sub-group of sub-fields from the plurality of sub-fieldsare used as data input instead of the video data words having N bits fora colour component, and wherein the motion vector calculation is donebased on the complete sub-field code words or based on said code wordsthat are formed from the entries in the sub-field code words of only asub-group of sub-fields from the plurality of sub-fields and the motionvector defines a trajectory along which corrected sub-field code wordswill be placed.
 12. Method according to claim 11, wherein for the casethat a motion vector calculation is done based on the complete sub-fieldcode words or for a sub- group of sub-fields, a gradient determinationstep is performed for comparing pixels in two successive frames, withthe gradient between two pixels being defined as the sum of thesub-field weights of those sub-fields of the sub-field code words orsub-group of the sub-field code words which have differenct binaryentries.
 13. Method according to claim 11, wherein for the determinationof corrected sub-field code words sub-field entry shifts are calculatedfor a given pixel based on the calculated motion vector and wherein thesub-field entry shifts determine which sub-field entry in the sub-fieldcode word of a given pixel need to be shifted to which pixel positionalong the direction of the motion vector.
 14. Method according to claim11, wherein it is used in a plasma display device for dynamic falsecontour compensation.
 15. Apparatus for performing the method of claim11, having a sub-field coding unit for each colour component video data,and corresponding compensation blocks for calculating correctedsub-field code words based on motion vector data, characterized in that,the apparatus further has corresponding motion estimators for each colurcomponent and that the motion estimators receive as input data thecomplete sub-field code words having N+X bits or code words that areformed from the entries in the sub-field code words of only a sub-groupof sub-fields from the plurality of sub-fields instead of the video datawords having N bits for the respective colour components.